livepatch/klp-build: report patch validation fuzz

Capture the output of the patch command to detect when a patch applies
with fuzz or line offsets.

If such "fuzz" is detected during the validation phase, warn the user
and display the details.  This helps identify input patches that may
need refreshing against the target source tree.

Ensure that internal patch operations (such as those in refresh_patch or
during the final build phase) can still run quietly.

Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Acked-by: Song Liu <song@kernel.org>
Link: https://patch.msgid.link/20260310203751.1479229-13-joe.lawrence@redhat.com
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

1 files changed, 19 insertions, 5 deletions

diff --git a/scripts/livepatch/klp-build b/scripts/livepatch/klp-build
index d628e2c86078..839f9b6bfe1f 100755
--- a/scripts/livepatch/klp-build
+++ b/scripts/livepatch/klp-build
@@ -360,11 +360,24 @@ check_unsupported_patches() {
 
 apply_patch() {
 	local patch="$1"
+	shift
+	local extra_args=("$@")
+	local drift_regex="with fuzz|offset [0-9]+ line"
+	local output
+	local status
 
 	[[ ! -f "$patch" ]] && die "$patch doesn't exist"
-	patch -d "$SRC" -p1 --dry-run --silent --no-backup-if-mismatch -r /dev/null < "$patch"
-	patch -d "$SRC" -p1 --silent --no-backup-if-mismatch -r /dev/null < "$patch"
+	status=0
+	output=$(patch -d "$SRC" -p1 --dry-run --no-backup-if-mismatch -r /dev/null "${extra_args[@]}" < "$patch" 2>&1) || status=$?
+	if [[ "$status" -ne 0 ]]; then
+		echo "$output" >&2
+		die "$patch did not apply"
+	elif [[ "$output" =~ $drift_regex ]]; then
+		echo "$output" >&2
+		warn "${patch} applied with fuzz"
+	fi
 
+	patch -d "$SRC" -p1 --no-backup-if-mismatch -r /dev/null "${extra_args[@]}" --silent < "$patch"
 	APPLIED_PATCHES+=("$patch")
 }
 
@@ -383,10 +396,11 @@ revert_patch() {
 }
 
 apply_patches() {
+	local extra_args=("$@")
 	local patch
 
 	for patch in "${PATCHES[@]}"; do
-		apply_patch "$patch"
+		apply_patch "$patch" "${extra_args[@]}"
 	done
 }
 
@@ -444,7 +458,7 @@ refresh_patch() {
 	( cd "$SRC" && echo "${input_files[@]}" | xargs cp --parents --target-directory="$tmpdir/a" )
 
 	# Copy patched source files to 'b'
-	apply_patch "$patch"
+	apply_patch "$patch" "--silent"
 	( cd "$SRC" && echo "${output_files[@]}" | xargs cp --parents --target-directory="$tmpdir/b" )
 	revert_patch "$patch"
 
@@ -817,7 +831,7 @@ fi
 if (( SHORT_CIRCUIT <= 2 )); then
 	status "Fixing patch(es)"
 	fix_patches
-	apply_patches
+	apply_patches "--silent"
 	status "Building patched kernel"
 	build_kernel "patched"
 	revert_patches